This invention relates to MOCVD of barrier and copper thin films for interconnects in semiconductor IC high-speed devices, and specifically to a method of enhancing adhesion properties of CVD copper.
Copper films which are formed by metal organic chemical vapor deposition (MOCVD) on metal nitride barriers, such as TiN or TaN, for example, which are also formed by MOCVD, do not exhibit good adhesive integrity, especially when the copper layer is grown in situ on a nitride layer or structure. The exhibited adhesion properties have prevented the application of copper CVD technology in IC manufacturing.
A great deal of research has been done in this area in order to improve the adhesion of copper to underlying barrier films. The related application and the cited prior art identify some improvements which have been made in this field, and include water vapor injection, barrier surface oxidation, barrier surface pre-treatment, and thermal densification. Of these improvements, only thermal densification has been shown to have practical application in providing reasonable throughput when copper is to be deposited in narrow trenches and vias. However, as thermal densification requires additional steps, thermal densification in copper CVD is relatively complex, and has lower throughput compared to conventional CVD.
Atomic Layer CVD (ALD) is a relatively new technology that has been adopted in semiconductor research, and is now being adopted for commercial IC production. ALD uses rapidly operating valves to deliver individual reactants into a deposition chamber. Each reactant deposits a mono-layer of material on the IC surface through chemical absorption, and reacts with a previously deposited mono-layer species to form the desired compound. The as-formed compound has a much higher density than could ever be achieved by conventional CVD. The ALD process also provides excellent step coverage. By carefully selecting precursors, multi-layered, or alternating layered, barrier metal films are formed, e.g., alternating TaN/SiN, TaN/TiN and TiN/SiN thin films, or other combinations thereof, may be easily formed. An entire film stack formed by ALD may be only 50 xc3x85 thick, and also exhibits excellent barrier properties.
The application of ALD is particularly useful in the fabrication of a barrier layer, such as a multi-layered TaN/TiN thin film stack. TaN thin films exhibit better barrier properties than does a stack of TiN, but does not provide adequate adhesion for subsequent layers, particularly copper thin film layers. Single thin film layers also have a grain structure that allows some diffusion along the grain boundaries. Thus, a TaN/TiN multi-layer thin film stack is desirable, provided that copper can be made to adhere to such a thin film stack.
U.S. Pat. No. 5,744,192, for Method of using water vapor to increase the conductivity of copper deposited with Cu(Hfac) TMVS, to Nguyen et al, granted Apr. 28, 1998, describes the use of water vapor to enhance the adhesive properties of copper thin films.
Nuesca et al., Surface effects in the MOCVD of copper, Mat. Res. Soc. Symp. Proc. Vol. 337, 1994, pp 177-188, describes the use of hydrogen to enhance the adhesive properties of copper thin films.
A method of adhering copper thin film to a substrate in an integrated circuit structure includes preparing a substrate, including forming active regions and trenches for interconnect structures; depositing a metal barrier layer on the substrate; depositing an ultra thin film layer of tungsten over the barrier metal layer; depositing a copper thin film on the tungsten ultra thin film layer; removing excess copper and tungsten to the level of the metal barrier layer; and completing the integrated circuit structure.
An integrated circuit having a copper interconnect therein formed over a layer of barrier metal includes a substrate, including active regions and trenches for interconnect structures; a metal barrier layer formed on the substrate, wherein said metal barrier layer is taken from the group of materials consisting of Ta, TiN, TaN, TaSiN and TiSiN, and formed to a thickness of between about 5 nm to 10 nm; an ultra thin film layer of tungsten formed on the barrier metal layer, said tungsten ultra thin film layer having a thickness of between about 1 nm to 5 nm; and a copper thin film layer formed on the tungsten ultra thin film layer to a thickness required to fill the vias and trenches, which is usually a thickness of between about 10 nm to 20 nm.
It is an object of the invention is to increase the adhesive properties of copper thin films on metal and metal nitride substrates.
Another object of the invention is to provide a method of depositing tungsten on a metal or metal nitride substrate to enhance the adhesion of a copper thin film to the substrate.